932502G / 0618
1. INTRODUCTION
Mode
Uncorrected
Spectrum
ZDT Corrected
Spectrum
ZDT Error
Spectrum
Off
(ZDT Disabled)
Yes
No
No
NORM_CORR
(ZDT–LTC Mode)
Yes
Yes
No
CORR_ERR
(ZDT–ERR Mode)
No
Yes
Yes
Table 1. ZDT Modes.
processed by the spectrometer. The corrected spectrum gives the best estimate of the total counts
that would have been in the peak if the system were free of dead-time effects. The uncertainty
spectrum can be used to calculate the counting uncertainty, channel by channel, in the corrected
spectrum.
NOTE
When the spectrometer is placed in ZDT mode, the throughput of the instrument is
reduced somewhat as extra processing must be done on the spectrum; therefore, if the
gamma-ray flux is not changing as a function of time, but absolute highest throughput
is desirable, you might wish to store only the LTC spectrum in the MCB memory.
1.6.2. NORM_CORR — ZDT and Uncorrected Spectra Stored
When the ZDT mode is set to
NORM_CORR
, the two spectra stored are the LTC spectrum and
the ZDT spectrum (corrected for the dead-time losses; real time only). Unfortunately, in the
analysis of the ZDT spectrum, the uncertainty of the measurement cannot be determined using
either spectrum.
NOTE
This mode is not useful for quantitative analysis if the counting rate varies significantly
during the measurement time, particularly if the user desires an accurate counting rate
and standard deviation calculation.
When you select the NORM_CORR mode, ORTEC
spectroscopy applications such as GammaVision
®
and ISOTOPIC ignores the ZDT
spectrum and analyzes the LTC spectrum as it would for the
Off
ZDT mode.
1.6.3. CORR_ERR — ZDT and Error Spectra Stored
In the
CORR_ERR
mode, the estimation of the statistical uncertainty is stored in place of the
LTC spectrum, and is referred to as the
error spectrum
(ERR). In this mode, the ZDT spectrum
is used to measure the counts in a peak, and the error spectrum is used to determine the uncer-
tainty of the measurement made in the corrected spectrum.
For example, if the area of a peak is measured in the corrected spectrum by summing channels
1000 to 1100, the variance of the measurement can be determined by summing the counts in
channels 1000 to 1100 in the error spectrum. Or, shown another way, the counts in channel
i
can
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